SWL @ RADIUS
SWL is the safe working load at the crane hook. It is also known as: rating, rated load or lift capacity. Radius is the reach, or distance from the center of rotation (center of crane pedestal) to the crane hook/center of gravity of the cargo. A higher radius will produce a larger tipping moment and cause the crane to topple if the SWL is not reduced. Even though pedestal cranes do not topple, the concept is the same.
Which is bigger, a 40 ton crane or a 100 ton crane? This is a misleading question since there is not enough information provided. SWL @ its RADIUS must be provided. A crane that can lift only 40 tons at a radius of 50 ft is twice as big as a crane that can lift 100 tons but at a radius of only10ft (40 x 50 = 2000 ton-ft, 100 x 10 = 1000 ton-ft tipping moment). So be careful and always specify the SWL @ RADIUS.
Note that whereas SWL is the safe working load at (below) the crane hook, SWLH is SWL + the weight of the hook block. SWLH is the load that the crane is subject to (if no motions are present or load factors applied) since, naturally, the crane lifts the SWL and the hook block.
ON-BOARD SWL
On-board lifts are those for which the crane lifts cargo from or lands cargo onto the crane mounting base structure. There is no relative motion between the lift/landing deck and the crane. An example would be a shipboard crane lifting a load off of its own deck.
OFF-BOARD SWL
Off-board lifts are those for which the crane lifts cargo from or lands it onto a deck which moves relative to the crane mounting base. An example would be a crane mounted on an offshore platform that is lifting a load from a work boat. The work boat moves vertically in the waves and drifts away and to the side. The vertical motion of the workboat imparts a shock load on the crane due to the relative motion between the crane hook and the cargo (cargo is falling on supply boat deck and hook is racing upward). The drifting workboat imparts detrimental side loads on the crane as the cargo/boat drifts to the side. And the drifting workboat imparts detrimental off-loads as the cargo/workboat drifts away from the crane. The vertical impact and horizontal loads significantly reduce the offboard SWL.